Method of producing acrylic nitrile



UnitcdStates Patentf) 2,920,100 rmrnooer-rnoneememime -LE Karl Meinel, Upper Bavaria, Germany,.iassignor'- to waclrfer-Ghemie G.mb:H.,- Munich -Germany, a firm of Germany Nol i-awing: ilplr tiams tember10, 1951 sermmassams The'present invention relates to amethod for the-production ofcacrylonitrile.

This application is a continuation-impart of my copending -application Serial No; 573,660gfiled-on March 26, 1956, now abandoned.

It is known that the thermal decomposition of acetylated -a-hydroxyearboxylicacid: nitriles. yields acetic acid and a-fl-unsaturated carboxylic acid nitrile s. 11'1" accordance with one process, the vapors of the starting materials are conducted at 540 C.-550 C. through an iron pipe filled with pieces of quartz, the feed rate being 247 grams per hour for each liter of reaction space. A yield of 36% is obtained. This is not a sufliciently high yield to answer commercial requirements. In another conventional method the thermal decomposition is carried out without catalysts at a temperature of 700 C. and above and a yield of 87 is purportedly obtained. The throughput of vaporous acetylated lactic acid nitrile is excessively high in this process, namely 6 kg. per hour per liter of reaction space. Accordingly, the process is technically impractical and, furthermore, the heat consumption is also too high.

The method according to the present invention enables low throughputs and temperatures to be utilized so that its commercial application is facilitated. It makes possible the use of very favorable reaction conditions which afiord conversions of as high as 90% to 97% without excessive formation of by-products so that yields of at least 97% can be obtained.

The method according to the invention for producing acrylic nitrile by thermal splitting of the vapor of acetylated lactic acid nitrile in the presence of catalysts at elevated temperature is essentially characterized by the use of metals of the first, fifth or sixth group of the periodic system or of platinum metals as catalysts. The vapors of the starting compound are preferably passed over the catalysts at a temperature of between 615 C. and 635 C., the throughput being preferably limited to not more than 1.5 kg. per hour, per liter of reaction space. The vapor of the acetylated lactic acid nitrile may contain minor amounts of an inert gas, for example, nitrogen. The dwell or length of time the vapors remain in the reaction chamber can also be controlled by the use of positive or negative pressures.

The catalysts mentioned above, whose use is an important object of this invention, can be employed in many ways, either individually, or in combination, or in the form of alloys. They may be employed in various forms such as, for example, in the form of shavings, sheet metal ribbons, wires, etc. They may be deposited on carriers which are provided for the metals and may also be applied in thin layers on metallic or nonmetallic, active or inactive parts of the reaction chamber. The metals acting as catalysts may be deposited in the form of a compound, for example, of an oxide, on the carrier and may be converted to their elementary state, for example,-bywmeans of hydrogen in the tube or coil which comprises-the- -reaction chamber. In ;-a simple embodiment of-ithe --invention,-a reaction tube isused which is made of the metal catalyst or an alloy-thereof; or to which? the catalyst' is applied as a thin layer. Not-all metals'of thefirst,--fitthand-sixth group .-of the periodic system orthe-platinum metals make equally' good-catalysts; Particularly, good results are obtained with molybdenum,tungstenand platinum-.- Of the alloys, irorr alloys have been found useful; however, they a are usuallyrsufficiently active-only if they contain 2%- to4% molybdenum. An alloy steel composed-of 70.5%.;Fe, 9.6% Ni, 17.7% Cr, and-22% Mo atlords a conversion of more than. 97 eta-reaction temperature of'615 C. at veryplittlelosses so thata-yield amounting-to 97% is obtained? Example 1 A 4 meter-alloy steel tube having an internal diameter oflO and a wall thi'ckne'ssf'ofi andformed' of an alloy containing 916%" nickel, 17.7 chromiumand 2.2% molybendum, the remainder being.iron, is wound into a spiral 30 cm. inl rigth and havingadiameter of about 8 cm. Anelect-r 'hea'ting'fel'eirient'"isplacedfinside the coil aiid', on the outer "side of "the" coil," are fitted suitable thermocouples. The entire apparatus is suitably insulated. The temperature at the center of the coils is held at 615 C. and a mixture of nitrogen and vaporized acetylated lactic acid nitrile are passed through the coiled tube at a rate of 450 grams per hour, the nitrogen in the mixture being held to a minimum. The vapors leaving the reactor are passed through an air-cooled condenser and finally through a series of three similar condensers which are ice-cooled. 97% of the acetylated lactic acid nitrile introduced are recovered as acrylonitrile and acetic acid. The conversion amounts to 97% and the yield of acrylonitrile obtained as well as that of acetic acid amount to 98%. The acrylonitrile and acetic acid are separated by distillation.

Example 2 A tube 65 cm. in length and 27 mm. internal diameter and made of steel containing 72% Fe, 18% Cr, 9.5% Ni was electrolytically plated internally with molybdenum. The tube was externally heated, electrically, so that the temperature as measured at the center of the tube is 624 C. Vaporized acetylated lactic acid nitrile is passed through the tube in admixture with a minimum amount of nitrogen at a rate of 450 grams of acetylated lactic acid nitrile per hour. The vapors leaving the tube are condensed and are separated into their components by distillation. A conversion of 90% is obtained and both acrylonitrile and acetic acid are obtained in a yield of 97%.

Example 3 Example 4 A copper tube of the dimensions as the tube in Example 2 was electrolytically plated inside with vanadium. Splitting of acetylated lactic acid nitrile at a temperature of 636 C. in the aforementioned tube produced a conversion of and a yield of acrylonitrile of 97.5%.

3 Example 5 A copper tube of the same dimensions as the tube in Example 2 was electrolytically plated inside with platinum in the conventional manner. Splitting of acetylated lactic acid nitrile in this tube at 620 C. produced a yield of acrylonitrile of 98% and a conversion of 86%.

What is claimed is:

1. Process for the production of acrylonitrile by the catalytic, vapor-phase, thermal decomposition of acetylated lactic acid nitrile, which comprises passing the vapors of acetylated lactic acid nitrile through a reaction zone containing a metal catalyst selected from the group consisting of molybdenum, tungsten, vanadium, platinum, and alloys of said metals, said vapors being passed through the reaction zone at a rate of at most 1.5 kg.- per hour for each liter of reaction space in the catalyst chamber while maintaining said reaction zone and said catalyst at a temperature of 615 C. to 635 C.

2. A method according to claim 1 in which the vapor of the acetylated lactic acid nitrile is diluted by an inert gas.

3. A method according to claim 1 in which the vapor of the acetylated lactic acid nitrile is diluted by nitrogen.

4. A method according to claim 1 in which the catalyst metals are applied to carriers.

5. A method according to claim 1 in which the catalyst metals are deposited on carriers as oxides and reduced to their elementary states in the reaction cham her.

6. A method according to claim 1 in which the catalyst metals are present in the wall of the reaction chamher.

7. A method according to claim 1 in which the catalyst metals are present in the form of pieces in the reaction chamber.

8. A method according to claim 7 in which the catalyst metals are in the form of shavings. Y

9. A method according to claim 7 inwhich the catalyst metals are in the form of sheet metal pieces.

10. A method according to claim 7 in which the catalyst metals are in the form of wire pieces.

References Cited in the file of this patent UNITED STATES PATENTS Farkas et a1. May 6, 1958 OTHER REFERENCES Berkman et a1.: Catalysis, pages 193, 365 and 488. 

1. PROCESS FOR THE PRODUCTION OF ACRYLONITRILE BY THE CATALYTIC, VAPOR-PHASE, THERMAL DECOMPOSITION OF ACETYLATED LACTIC ACID NITRILE, WHICH COMPRISES PASSING THE VAPORS OF ACETYLATED LACTIC ACID NITRILE THROUGH A REACTION ZONE CONTAINING A METAL CATALYST SELECTED FROM THE GROUP CONSISTING OF MOLYBDENUM, TUNGSTEN, VANADIUM, PLATINUM, AND ALLOYS OF SAID METALS, SAID VAPORS BEING PASSED THROUGH THE REACTION ZONE AT A RATE OF AT MOST 1.5 KG. PER HOUR FOR EACH LITER OF REACTION SPACE IN THE CATALYST CHAMBER WHILKE MAINTAINING SAID REACTION ZONE AND SAID CATALYST AT A TEMPERATURE OF 615*C. TO 635*C. 